1. Field of Invention
This invention relates to battery chargers and more particularly to methods and apparatus for charging batteries in a system of batteries.
2. Description of Related Art
Multi-battery and multi-battery-bank battery systems are finding increased usage. Usage of such systems often requires charging of batteries or banks of batteries and many ways of charging have been developed. One way is to employ a single charger with a plurality of diode-isolated output stages. Another way is to employ a plurality of individual chargers all enclosed within a single enclosure. Another way is to employ a single common primary (high voltage) side architecture with either a single or multiple transformers and a plurality of secondary side isolated or non-isolated rectifier stages. Another way is to provide a single main charger module with a plurality of secondary side post regulator circuits for auxiliary battery banks for individual bank control. Another way of charging multiple batteries or battery banks is to use a single full power charger with time-domain multiplexed output stage connectable to a plurality of batteries or battery banks.
Traditional marine style multi-bank battery chargers employ the diode-isolated method described above. A diode-isolated system typically involves the use of two or more diodes connected together to prevent current flowing from one battery to another while permitting current to flow through both or all diodes at the same time allowing all batteries or battery banks to be charged at the same time. In such a system, current from the battery charger is split or shared approximately equally between batteries or battery banks when all the batteries or battery banks being charged have approximately the same state of charge. If any one battery has a lower state of charge than the other batteries or battery banks in the system, that battery or battery bank receives most of the charging current until its state of charge is approximately equal to the next lowest charged battery and then two batteries draw current from the charger and so on. This process continues until all batteries or battery banks are charged but it places an increasing load on the charger because charging is done on all of the batteries simultaneously.
Unfortunately, diode-isolated systems are not readily adaptable to permit charging to be specifically controlled for any particular battery. This limits the ability of the batteries or battery banks to be efficiently charged and often requires that the same type of battery be used at every battery or battery bank position in the battery system since the use of the same charging methodology with batteries of different battery chemistries will often result in one battery being overcharged while another battery remains undercharged.
The use of multiple chargers is wasteful in that often one battery is severely discharged while another may be nearly fully charged such that only 1/n of the available power is available for charging an individual bank.
The single common primary scheme described above often requires that each of the secondary side rectifiers be rated for the full power of the charger and usually such systems fail to provide for individual control of current and voltage to any given battery or battery bank.
Systems employing the single main charger and secondary side post regulator circuits require a plurality of secondary side control circuits. Often these systems are configured such that there is a full power high priority bank with a plurality of reduced power outputs.